Metering pump with a rotary valve responsive to electrical signals from the contact between a fluid responsive shuttle and dual probes

ABSTRACT

A metering device contains a rotor which defines elongate chamber, there being a shuttle contained within the chamber movable between two terminal end positions. Frusto-conical surfaces defined on the rotor cooperate with annular members defining corresponding seats. One passage extends from one end of the chamber to one frusto-conical surface, and another passage extends from the other end of the chamber to the other frusto-conical surface. Each annual element defines a respective inlet and outlet for fluid and a shuttle is present within the chamber. As the rotor rotates, the shuttle effects a shuttling movement thus measuring dispensed volumes of fluid. A sensor is provided to detect physical contact of the shuttle with the end of the chamber to cause the rotor to advance.

RELATED U.S. APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO MICROFICHE APPENDIX

Not applicable.

1. Field of the Invention

The present invention relates to a metering device.

2. Background of the Invention

Metering devices have been proposed before. One type of metering deviceis used to control the dispensing of a liquid or fluid, which may besupplied to the metering device under pressure, and the metering deviceacts to dispense a precisely predetermined quantity of the liquid orfluid. An alternative form of metering device monitors the flow rate ofliquid or fluid passing through the device.

The present invention seeks to provide a metering device which may beused for either of the purposes outlined above.

It is to be noted that it has been proposed previously to use meteringdevices to control the relative metering of two or more reactive liquidswhich together form a two-component reactive system in ratio to eachother prior to their being mixed and dispensed. Examples of suchtwo-component reactive systems are epoxies, polyurethanes, acrylics,silicones and polysulphides with their typical functions as sealing,bonding, encapsulating, coating, mould making, moulding and electricalor thermal insulating. Needless to say, such materials are currentlyused in nearly every type of production circumstance and across a verybroad range of industries.

Despite their current importance and level of application, it should beappreciated that the use of multi-component reactive liquid systems,despite all the advantages, is still the subject of considerablescepticism by designers and production engineers. This is for the simplereason that “state of the art”shot or flow metering, mixing anddispensing machinery does not assure that the correct relativeproportioning of the two or more chemical components takes place withina tolerance, or even that it takes place at all. Mixed resin colorchanges, such as yellow and blue mixing to become green, can sometimesbe used for visually checking that a degree of correct proportioning hastaken place, but many premixed components are of approximately the samecolor and therefore no change is identifiable visually. Also, mixedproduct testing can be done on a random basis but if it is, it is not acheck on the total product. Therefore, with the fact that “state of theart”machines can, and do, partially fail, fluctuate in failure,progressively fail through wear or totally fail, this is an area wherethe end mixed product specification is unqualified and where part ortotal failure of the end product remains a hazard. The scepticism ofproduction engineers concerning this type of process is understandable,especially since quality assurance standards demand total control. Onlysectors of the aircraft industry can presently justify a costly onehundred percent quality assurance system whereby part of a product batchis applied to a structure with its position in a structure beingrecorded while the other part of the batch is laboratory tested,rejected or approved, documented and stored.

While two or more component reactive systems have been mentioned, thereare other areas of great significance where metering takes place such aswith multiple chemical stream processes or in a single component meteredshot application as, for instance, with grease being placed within abearing. In all applications, the need remains to assure performance butin some applications the need is to ensure the avoidance of acatastrophe through product failure in the field.

EP 0,646,776A discloses a metering device for fluids which isspecifically intended for use in a proportioning and mixing apparatusfor a two-component material. The device is an oscillatory device.

In the arrangement disclosed in EP 0,646,776A, a housing is providedhaving a fluid inlet and a fluid outlet. A passage, within the housing,forms a communication between the fluid inlet and the fluid outlet. Arotary member is provided located within the passage which effectivelyseals the passage, the rotary member defining a diametrically extendingbore which, in two rotational positions of the rotary member, becomesaligned with the passage. A ball is contained within the bore, and isadapted to form a sealing engagement with each of two seats provided forthat purpose, at opposed ends of the bore.

In use of the metering device, shown in EP 0,646,776A, after theapparatus has been primed, so that the flow passage Within the housingand the bore within the rotary member are both full of liquid to bedispensed, when the rotary member is moved to a first position, with theball engaging the seat located closest to the fluid inlet, fluid willflow through the fluid inlet and into the bore, pushing the ball awayfrom the seat so that the ball moves axially of the bore until the ballengages the other seat. Fluid that was initially contained with the boreis thus expelled into the part of the passage adjacent the fluid outletso that fluid is forced out of the metering device. When the ballengages the seat which is located adjacent the fluid outlet, no furtherfluid can flow through the device.

The rotatable element is then rotated through 180° so that the ball isagain located at a position adjacent the fluid inlet. The cycle ofoperation then repeats. The rotatable element is rotated at such a ratethat it is anticipated that the ball completes the journey from one seatto the other seat on every occasion that the rotatable element is in aposition such that the bore is aligned with the passageway.

It is often difficult to maintain appropriate seals in the arrangementdisclosed in EP 0,646,776A, bearing in mind that the ball is subjectedpermanently to the source of the fluid under pressure.

BRIEF SUMMARY OF THE INVENTION

The present invention seeks to provide an improved metering device.

According to this invention there is provided a metering device, themetering device comprising means defining a chamber having two opposedends comprising an elongate bore, each end of the elongate boreaccommodating a respective probe, the inner ends of which bound thechamber, at least one probe being axially adjustable in position, eachprobe having electrically conductive means extending from the inner endface of the probe, there being inlet means to enable fluid to enter oneend of the chamber and inlet means to enable fluid to enter the otherend of the chamber, there being outlet means to enable fluid to exitfrom said one end of the chamber, and outlet means to enable fluid toexit from the other end of the chamber, there being a shuttle providedwithin the chamber at a position intermediate said two ends, at leastthe opposed ends of the shuttle being electrically conductive, theshuttle acting sealingly to separate the two ends of the chamber, theshuttle being movable between two terminal positions, each probe beingresponsive to physical contact with the shuttle to generate a respectiveelectrical signal when the shuttle reaches each one of said two terminalpositions, there being valve means to control fluid flow which, in onecondition, permit the entry of fluid into one end of the chamber andpermit the simultaneous exit of fluid from the other end of the chamberand which, in another condition, permit the entry of the fluid into saidother end of the chamber and permit simultaneous exit of fluid from thesaid one end of the chamber, there being control means adapted to changethe condition of the valve means on receipt of a said electric signalgenerated when the shuttle reaches a said terminal position.

Advantageously the inlet and outlet means incorporate ports in theside-wall of the chamber and the inner-most end of each probe whichdefines the chamber is configured to permit the entry or exit of fluidif the inner-most end of the probe is aligned with a said port.

Conveniently the inner-most ends of the probes which defines the chamberare of reduced diameter.

Preferably the shuttle has a central part which is a sealing sliding fitwithin the chamber, and two terminal end parts of reduced diameter.

Preferably the valve means is constituted by a rotor assembly, the rotorassembly being such that in one position thereof a fluid flow isestablished between a first inlet, and one end of the chamber, and isalso established between the other end of the chamber and a firstoutlet, whereas in a second position of the rotor assembly fluid flow isestablished between a second inlet and the other end of the chamber, andbetween said one end of the chamber mid a second outlet, the rotorassembly being movable, by motor means, between said positions inresponse to a signal generated when the shuttle reaches one of saidterminal positions.

Advantageously, the device comprises a housing provided with first inletmeans and second inlet means, and also provided with first outlet meansand second outlet means, the rotor assembly being rotatable within thehousing, the motor assembly having an element defining the said chamber,and also defining a first passage which extends from one end of thechamber and a second passage which extends from the other end of thechamber, the rotor assembly, in one position, having the first passagealigned with and in communication with said first inlet and said secondpassage aligned with and in communication with said first outlet, andbeing rotatable to a second position in which said first passage isaligned with and in communication with said second outlet and saidsecond passage is in alignment with and in communication with saidsecond inlet the said passages being substantially sealed in otherpositions of the rotor.

Conveniently the rotor has a first plurality of passages located to bealigned individually, on rotation of the rotor, with the first inlet andsecond outlet, and a second plurality of passages located to be alignedindividually, on rotation of the rotor, with the second inlet and firstoutlet.

Preferably said first plurality of passages and said second plurality ofpassages each comprise an odd number of passages, between five and nine.

Conveniently the rotor assembly has a body portion, the body having acentral region with a relatively large diameter, the body tapering, fromthe central region of large diameter, towards opposed ends of the body,each tapering part of the body being snugly received within aco-operating frusto-conical or tapering opening formed in a respectiveannular element, each annular element being provided with a respectivesaid inlet and a respective said outlet.

Preferably said annular elements are retained within a housing, andmeans are provided to apply force to the annular elements to bias theelements inwardly into secure sealing contact with the tapering parts ofthe body.

Conveniently the force applying means comprise means to apply hydraulicpressure to the end faces of the annular elements.

In an, alternative preferred embodiment of the invention the meteringdevice comprises a fixed body, the fixed body defining said chamber anddefining first inlet means, second inlet means, first outlet means andsecond outlet means, each of said inlet means and outlet meansterminating at an exterior surface of the body at a position adjacentthe termination, at the exterior of the body, of a respective passageleading to a respective end of the said chamber, the rotor assemblybeing mounted on the exterior of the body, the rotor assembly havingmeans which, in one position of the rotor assembly, create acommunication between the first inlet and the respective passage, andthe second outlet and the respective passage and which, in an alternateposition of the rotor assembly establish a connection between the secondinlet and the respective passage, and the first outlet and therespective passage but which, in other positions of the rotor assembly,substantially seal said inlets and said passages.

In a further embodiment the valve mean comprise individual valvesassociated with said inlet means and outlet means.

In one arrangement one end of the chamber is connected to a valve, thevalve being adapted to connect said one end of the chamber selectivelyto either a source of fluid to be introduced to the chamber, or to anexit conduit, the other end of the chamber being connected to a secondcorresponding valve adapted to connect the said other end of the chamberselectively to either an exit conduit, or a source of fluid to beintroduced to the chamber.

In another arrangement each end of the chamber is associated with arespective entry conduit and exit conduit, each conduit having arespective valve to control flow in the conduit.

Preferably a sensor is provided to sense fluid leaking from the deviceand to generate a signal indicative of the fluid leakage detected.

Conveniently the device further incorporates stop valve means in a flowpath for fluid leaving the chamber, the stop valve means being adaptedto be opened only when the valve means permit flow from the chamber tothe flow path.

The invention also relates to a metering device arrangement whichincorporates two metering devices as described above, each meteringdevice being associated with a reservoir of liquid to be metered by themetering device, the outlets of the metering devices being directed to amixer adapted to mix liquids from the reservoirs when metered by thedevices, the control means of the metering devices each providingsignals to a supervising control arrangement, the supervising controlarrangement being adapted to stop the operation of one metering devicein response to a ceasing of the operation of the other metering device.

Preferably the control means of each metering device pass a signal tothe supervising control means on receipt of a signal generated when ashuttle of the respective metering device reaches a respective terminalposition, the supervising control means incorporating counters adaptedto count the signals, and means to compare the counts present in thecounter, the supervising control further including means adapted to stopoperation of the metering devices if an output from the comparatorexceeds a predetermined threshold.

Advantageously means are provided to re-set the counters when the countin a counter exceeds a predetermined threshold.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In order that the invention may be more readily understood and so thatfurther features thereof may be appreciated, the invention will now bedescribed, by way of example, with reference to the accompanyingdrawings.

FIG. 1 is a cross-sectional view of the main part of a metering devicein accordance with the invention.

FIG. 2 is a view illustrating the body of FIG. 1, again in section,incorporating, in block diagram form, additional components of acomplete metering device.

FIG. 3 is a sectional view corresponding to FIG. 2, illustrating thevalve components of the device in an alternative position.

FIG. 4 is a block diagram illustrating two devices of the typeillustrated in FIGS. 1 to 3 incorporated in an apparatus for dispensingtwo fluids.

FIG. 5 is sectional view of the main part of an alternative embodimentof the metering device.

FIG. 6 is a diagrammatic sectional view of another metering device.

FIG. 7 is a diagrammatic sectional view of yet another metering device.

FIG. 8 is a diagrammatic view illustrating a typical embodiment of theinvention.

FIG. 9 is a diagrammatic view corresponding to FIG. 8 illustrating amodified embodiment of the invention.

FIG. 10 is a diagrammatic view of an embodiment of the invention similarto that shown in FIG. 1 incorporating a stop valve.

FIG. 11 is a schematic view illustrating two metering valves of the typeshown in FIG. 1 incorporating a common stop valve.

FIG. 12 is a schematic view illustrating a further embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Referring initially to FIG. 1 of the accompanying drawings, the mainpart of a metering valve comprises a housing 1 constituted by a shorttube 2 provided with two end plates 3, 4, each end plate being securedto a respective end of the tube 2 by a plurality of screws 5.

The tube 2 is provided with a plurality of apertures formed in the sidewall thereof, there being two diametrically opposed apertures 6, 7located adjacent the end plate 3, and two further diametrically opposedapertures 8,9 located adjacent the end plate 4. In the embodimentillustrated, the apertures 6 and 8 are axially aligned, and theapertures 7 and 9 are axially aligned.

The end plate 3 is provided with a centrally located aperture 10, theaperture 10 communicating with a seat 11 directed towards the side ofthe end plate 3 facing towards the interior of the tube 2. The seat 11is of circular form, having a diameter slightly greater than thediameter of the aperture 10. The seat 11 itself communicates with afurther seat 12 which is formed within the face of the end plate 3directed towards the interior of the tube 2, the seat 12 again being ofcircular form and having a diameter greater than that of the seat 11.

The end plate 3 is additionally provided with a screw-threaded throughpassage 13 located between the aperture 10 and the periphery of the endplate 3.

The end plate 4 has a construction which is a mirror image of the plate3, and the same parts are identified with the same reference numerals.

It will be appreciated that the housing 1 defines a cavity 14 which isbounded by the tube 2 and the end plates 3,4. Received within the cavityare two annular elements 15,16. The annular elements 15,16 each have anouter periphery that has a diameter which is substantially equal to theinternal diameter of the tube 2. Two parallel grooves 17,18 are formedin the outer periphery of each of the annular elements 15,16 and asealing “O”-ring of resilient material 19 is received within the groove17 and a corresponding sealing ring 20 is received within the groove 18.

The annular elements 15,16 each define a respective central opening 21of frusto-conical or tapering form, with the opening being directedtowards the center of the cavity 14.

At diametrically opposed positions, the outer-most peripheral surface ofthe annular element 15, and also the annular element 16, is providedwith internally threaded openings 22,23 which communicate, respectively,with bores 24,25 which open into the central tapering opening 21 formedin the annular member. Received within the threaded opening 22 is aconnector 26 which passes through the aperture 6 formed in the pipe 2,and received within the opening 23 is a connector 27 which passesthrough the aperture 7 formed in the pipe 2.

It is to be noted that the annular elements 15,16 are of mirrorconfiguration.

A rotor assembly 30 is provided having a substantial portion receivedwithin the chamber 14 defined by the housing 1. The rotor assembly 30comprises two outwardly directed opposed trunions 31,32. An axial bore33 extends through the trunions 31,32, the terminal bore portions 34,35being threaded. The trunions 31,32 support a body 36 which is locatedwithin the cavity 14, the body 36 having a central region with arelatively large external diameter, the body tapering to a smallerdiameter, from that central region towards the trunions 31,32, so thatthe body is received within the frusto-conical, or tapering openings 21,formed in the annular elements 15 and 16. The nature of thefrusto-conical openings 21 and the tapering faces of the body 36 aresuch that the openings 21 are in substantially sealing contact with thetapering faces of the body 36. The body 36 is provided, at the junctionbetween the tapering faces and each trunion with a larger diameter seat37, which corresponds with and lies adjacent the seat 12 of the endplate 3, and a smaller diameter seat 38 which lies adjacent andcorresponds with the smaller diameter seat 11 of the end plate 3.Resilient seals 39 are provided which are located within the seats 12,38, and bearings 40 are provided located in the seats 11 and 38.

The body 36 is thus mounted for rotation about the axis of the trunions31, 32 in the housing 1.

The body 36 defines a first laterally extending passage 41 which extendssubstantially radially from a central part of the bore 33, and extendsthrough the body 36 and is, in one rotational position of the body 36,(as shown in FIG. 1) in alignment and communication with the bore 24associated with the connector 26 of the annular element 16. The body 36is also provided with a second radially extending passage 42 which, inthe said one rotational position of the body 36 extends from a centralportion of the bore 33 radially outwardly to be in alignment and incommunication with the bore 25 associated with the connector 27 of theannular element 15.

It is to be appreciated that the arrangement is such that on rotation ofthe body 36 by 180°, the passage 41 will be aligned with the bore 25associated with the connector 27 of the annular member 16, whereas thepassage 42 will be aligned with the bore 24 associated with theconnector 26 of the annular element 15.

A probe 50 is provided which is mounted within the axial bore 33 of thetrunion 31. The probe 50 is of elongate form, and has a terminal portion51 having a diameter which is less than the diameter of the axial bore33. Adjacent the terminal portion 51, the probe has a portion 52 havinga diameter which is substantially equal to the internal diameter of thebore 33. An annular groove 53 is provided adjacent the junction betweenthe terminal portion 51 and the central portion 52 of the probe 50. Thegroove 53 contains a resilient sealing “O-ring”54.

At the other end of the probe, the exterior of the probe is providedwith threading 55. The threading is adapted to engage with the threadedend portion 44 of the axial bore 33. A lock nut 56 is also providedwhich engages the threading 55. It is to be appreciated that theposition of the probe relative to the main part of the rotatableassembly 30 may therefore be adjusted.

The probe incorporates a pair of mutually insulated electricallyconductive elements 57,58 which terminate at an end face 59 defined atthe end of the relatively small diameter terminal portion 51.

A probe 60 is provided which is associated with the trunion 32. Thedesign of the probe 60 generally corresponds with the design of theprobe 50, and consequently the probe 60 will not be described in detail.

Because the positions of the probes relative to the main part of therotatable assembly may be axially adjusted, the volume of the chamberdefined by the part of the axial bore 33 between the inner ends of theprobes may be selected to be a desired volume. Of course, even if onlyone probe was adjustable the volume of the chamber may be adjusted.

Located within the chamber defined by the part of the bore 33 betweenthe two probes is a shuttle 61. The shuttle has a main cylindricalportion 62 with a diameter equal to the diameter substantially of thebore 33, and two terminal portions 63,64 of reduced diameter. Thediameter of the terminal portion 63, 64 may be the same as the diameterof the terminal portion 51 of the probe 50. The shuttle is a sliding,yet substantially sealing fit within the bore 33.

It is to be appreciated that a relatively small volume pressure chamber70 is defined between the inner face of the end plate 3, and an exposedside face of the annular element 15. The pressure chamber 70communicates with the threaded passage 13. A similar pressure chamber 71is defined which is associated with the end plate 4 and the annularelement 16.

Hydraulic fluid under pressure, may be supplied to the pressure chambers70 and 71, through connectors connected to the threaded passages 13 inthe end plates 3 and 4, thus applying a force thrusting or biasing theannular elements 15 and 16 axially inwardly relative to the housing 1,thus bringing the tapering faces of the annular elements 15,16 whichdefine the frusto-conical opening firmly into engagement with theexterior tapering faces of the main body 36 of the rotatable assembly30. The seals 39 provided in the seats 37 and 12 prevent this hydraulicfluid from escaping. The seals 19,20 minimize the risk of the fluidtraveling axially, within the housing, from the pressure chambers 70,71. The apertures 6, 7 and 8, 9 provided in the tube 2 permit a slightaxial movement, relative to the axis of the tube 2, of the connectors26, 27 which are associated with the annular elements 15,16. Alternatemeans of applying a force to the annular elements 15,16 may be used, inother embodiments of the invention, to bias the annular elementsinwardly.

In the described embodiment the tube 2 is provided with a furtherthreaded opening 72 which communicates with a space 73 defined betweenthe adjacent faces of the annular members 15 and 16 to receive aconnector to drain away any fluid that weeps into the space 73.

The opening 72 will be connected to a sensor adapted to sense the fluidthat weeps into the space 73. The amount of weeping fluid represents thedegree of wear of the components of the metering valve. The sensor maygenerate a signal when the amount of weeping fluid or the rate ofweeping fluid flow reaches a predetermined threshold. The signal may beused to indicate that the metering valve should be services or, inparticularly sensitive applications, the signal may be used to terminateoperation of the metering valve.

At this stage it is important to note that in this embodiment theshuttle 61 is formed an electrically conductive material or, at least,has end faces of the reduced diameter terminal portions 63, 64 formed ofconductive material. The arrangement is such that should the shuttle 61contact the end face 59 of the probe 50, it will complete an electriccircuit between the two mutually insulated electrically conductiveelements 57, 58. Similarly, should the shuttle 61 contact the end faceof the probe 60, it will again complete an electric circuit.

In a modified embodiment of the invention the entire shuttle may beconductive, and also the body 36 of the rotatable assembly. Each probewill have a single conductive contact provided at the reduced diameterend. When the shuttle touches the probe, a circuit which includes themain body 36 of the rotor assembly, the shuttle and the probe iscompleted.

Referring now to FIGS. 2 and 3 of the accompanying drawings, it is to beappreciated that the housing 1, as described above, with reference toFIG. 1, will be associated with a motor 80 which is adapted to rotatethe rotor assembly 30. The motor, in this embodiment, is adapted torotate the rotor assembly 30 step-wise by precisely 180°. The motor isactivated by a control 81. The control 81 is adapted to receive a signalfrom the probe 50 when the shuttle 61 contacts the probe 50, and also isadapted to receive a signal from the probe 60 when the shuttle 61contacts the probe 60. The control arrangement may be associated with ameter 82, which may be a flow rate meter.

When the illustrated arrangement is in use, the arrangement is “primed”,and the connectors 26 of the annular elements 15 and 16 are bothconnected to a source of fluid to be metered, whereas the connectors 27associated with the annular elements 15 and 16 are each connected to apoint where the dispense fluid is to be utilized.

In a cycle of operation of the illustrated device, initially the rotorassembly 30 is in the position illustrated in FIG. 2 in which thepassage 42 is aligned with a first fluid inlet in the form of the bore24 associated with the connector 26 of the annular element 15 which isacting as a fluid entry conduit leading to an entry port in the sidewall of the chamber defined by the axial bore 33, whereas the passage 41is aligned with a first fluid outlet, the bore 25 associated with theconnector 27 of the annular element 16, the bore 25 acting as an exitconduit for fluid and defining an exit port in the side wall of thechamber defined by axial bore 33. In the condition illustrated in FIG.2, fluid has entered the central portion of the axial bore 33, movingthe shuttle 61 towards the left. The terminal portion 63 of the shuttle61 has just touched the end of the probe 60. This causes the completionof an electrical circuit, and consequently a signal is provided to thecontrol 81. The control 81 consequently actuates the motor 80 to rotatethe rotor assembly 30 by 180°.

As the rotor assembly 30 rotates, the passages 41 and 42 are sealed.

The rotation of the rotor assembly 30 through 180° brings the passage 41into alignment with a second fluid inlet in the form of a bore 24associated with the connector 26 of the annular element 16, and bringsthe passage 42 into alignment with a second fluid outlet in the form ofthe bore 25 associated with the connector 27 of the annular element 15.Pressurized fluid entering the illustrated arrangement through theconnector 26 of the annular element 16 is introduced into the annularspace that surrounds the projecting reduced diameter terminal portion 63of the shuttle 61, and the reduced diameter end portion of the probe 60which corresponds with the portion 51 of the probe 50. Thus the fluid,under pressure, acts on the surface area of at least part of the end ofthe shuttle 61, so as to move the shuttle 61 to move towards the rightas shown in FIG. 2. The shuttle is shown in FIG. 3 as having moved tothe right with the terminal portion 64 of the shuttle against and incontact with the end face 59 of the probe 50.

As the shuttle moved to the right, a precisely predetermined volume offluid which was initially contained within the part of the bore 33between the shuttle 61 and the probe 50 was caused to flow out of theconnector 27 associated with the annular element 15.

When the shuttle reaches the end position, as shown in FIG. 3, anelectrical signal is provided from the probe 50 to the control 81 whichagain causes the motor 80 to rotate the rotor assembly 30 by 180°. Therotor assembly 30 is thus returned to the position as shown in FIG. 2.Fluid then enters the arrangement through the connector 26 associatedwith the annular element 50, causing the shuttle to move to the left asshown in FIG. 2, whilst simultaneously discharging another preciselypredetermined volume of fluid through the connector 27 associated withthe annular element 16.

The meter 82 receives signals from the control 81, and may provide anoutput indicating the flow rate, in terms of volume per period of time,or may provide an output in terms of the total volume passed through theillustrated arrangement since initiation of operation, or sinceinitiation of an operating cycle.

It is to be understood that should, for any reason, the shuttle 61 notcomplete a full stroke when shuttling between the end faces of theprobes 50 and 60, the shuttle will not make contact with the terminalportion of the appropriate probe, and consequently the control 81 willnot receive a signal to activate the motor 80. In this case thearrangement will automatically stop and thus no further fluid will bemetered.

The described embodiment of the invention has the advantages that thefaces of the tapering openings of the annular elements are biased orpressed, by a hydraulic force, firmly against the conical faces presenton the rotor, thus providing an effective seal across the abutting faceareas. The rotor itself acts as a valving member, since when the rotoris in a position such that either the passage 41 or the passage 42 (inthe described embodiment) is aligned with a fluid entry or a fluid exitflow is permitted, whereas if the passage is in another orientation, theend of the passage on the exterior of the frusto-conical surface of therotor is effectively seated by tapering opening the frusto-conical seatformed within the annular member.

Referring now to FIG. 4 of the accompanying drawings, a first device 100of the type described above is illustrated together with the associatedmotor 101 and control 102, adapted to meter fluid from a reservoir 103to a mixer 104.

A second device 105, again of the type described above, with anassociated motor 106, and a control 197 is also provided adapted todispense fluid from a second reservoir 108 to the mixer 104. The mixer104 is provided with an outlet 109 to direct the mixed liquids which mayform a two-component material to an appropriate point.

Each of the control arrangements 102, 107 is connected to a supervisingcontrol arrangement 110. The supervising control arrangement 110incorporates two counters 111, 112, with the counter 111 being connectedto the control 102, and adapted to count the control pulses generated bythe control 102 as supplied to the motor 101, and with the counter 112connected to the control 107 adapted to count the control pulsesgenerated by the control 107 and supplied to the motor 106.

It is to be appreciated that the two fluids may not be mixed in equalproportions, and consequently it may be intended that for example, thevalve 100 may dispense five times as much fluid as the valve 105,meaning that when the apparatus is working in the intended manner, thecounter 111 will achieve a count which is five times as high as that ofthe counter 112. The outputs of the two counters are supplied to adelaying comparator 113. The comparator compares the counts present inthe two counters, but only after a predetermined period of operation sothat the comparator does not compare the counts when both the countershave recently been re-set to zero.

The output of the comparator is provided to a threshold circuit 114which determines whether the ratio between the counts present in thecounter 111 and 112 is within an acceptable range. If the ratio of thecounts within the two counters 111, 112 is not within an appropriaterange, which will be indicative of the fact that one of the counters hasstopped operating, due, for example, to jamming or incorrect operationof the shuttle of the associated valve, the threshold circuit 14 willprovide an output to a stop circuit 115. The stop circuit 115 isconnected to the control 102 and the control 107, and will provide theeffect of stopping the associated motors 101, 106.

Consequently, if the metering devices are being utilized to mix twofluids with a precisely predetermined ratio of mix, should either of thedevices fail for any reason, the supply of liquids to the mixer will beterminated, meaning that no incorrectly mixed material will bedispensed.

It is to be understood that the delay present in the delay comparator113 should be shorter than the period of time taken for the meteredmaterial to travel from the valves 101, 105 to the mixer 104.

In order to prevent the counts in the counters 111, 112 becoming toolarge, one counter 112 is associated with a threshold circuit 116adapted to determine when the count in the counter 112 reaches apredetermined threshold. When the threshold is reached, the thresholdcircuit 116 provides an output to a re-set circuit 117, which thenre-sets the counters 111 and 112 to zero.

FIG. 5 illustrates a modified form of housing 120 that constitutes analternative embodiment of the invention. In this embodiment of theinvention, trunions and probes are provided similar to the trunions andprobes of the embodiment described above, but, in this embodiment, thetrunions and probes are mounted to be stationary, and part of a housingis intended to rotate.

Thus, as shown in FIG. 5, the assembly comprises a fixed unit 121, whichcomprises outwardly directed trunions 122, 123, each provided with anadjustably positioned probe 124,125, the probes extending into a chamber126 defined within a bore extending through the trunions 122,123. Thecentral part of the bore defining the chamber 126 is surrounded by fixedelements 127, 128, each of frusto-conical form, the elements havingtheir narrower ends immediately adjacent each other.

Each of the frusto-conical elements 127,128 is provided with twodiametrically opposed passages 130,131, which each communicate with thechamber 126. The passages terminate at diametrically opposed points inthe tapering outer face of the elements 127, 128.

The frusto-conical element 127 is associated with a further element 132,whilst the frusto-conical element 128 is associated with a furtherelement 133 of corresponding design, with the further elements 132, 133extending axially outwardly away from the frusto-conical elements 127,128 and surrounding the trunions 121,123. The further element 132defines an inlet passage 134 for fluid to be metered, which is connectedto a connector 135. The inlet passage 134 has its end 136 located on thetapering face of the frusto-conical element 127 at a point 136 adjacentbut slightly spaced from the point at which the passage 131 intersectsthe tapering face. The further element 132 also defines an outletpassage 137 for fluid to be dispensed which is associated with aconnector 138, the outlet passage 137 terminating at a point 139adjacent but slightly spaced from the point at which the passage 130intersects the tapering face of the frusto-conical element 127.

A rotor assembly 140 is provided carrying members 141,142, each of whichdefines a frusto-conical seat receiving, in a sealing manner, one of thefrusto-conical members 127, 128. The members 141, 142 will be biasedapart, and thus into firm engagement with the frusto-conical elements127, 128 by a hydraulic fluid supplied to the annular space between themembers 141, 142 or by a spring located between the members 141, 142.Part of the frusto-conical seat is recessed 143, and the arrangement issuch that when the rotor assembly 140 has a predetermined rotationalposition, the recess 143 forms a communication between the end 136 ofthe inlet passage 134, and the passage 131 leading to the chamber 126.When the rotor assembly is in this position, it is to be appreciatedthat a corresponding recess 144 provided on the element 142 forms acommunication between the other end of the chamber 126 and an outlet forfluid to be dispensed. When the rotor assembly 140 is rotated by 180°,it is to be appreciated that the situation is reversed, and the recess143serves as a communication between the chamber 126 and the outletconnector 138, whereas the recess 144 will serve as a communicationbetween the other end of the chamber 126 and an inlet connector 146.

It is to be observed that a shuttle 145 is provided located as aslidable, but sealing fit, within a part of the bore that extendsthrough the trunions 122, 123 which serves to separate the part of thechamber 126, associated with the passages 130, 131 in the member 141from the opposite end of the chamber 126 associated with thecorresponding passages provided in the member 142.

As in the previously described embodiment of the invention, each probe124, 125 is provided with electrically conductive means adapted to beengaged by an end portion of the shuttle 145, as the shuttle completes astroke during operation of the device, and consequently the arrangementillustrated in FIG. 5 may be used with a motor and control arrangementof the type described in FIGS. 2, 3 and 4.

As can be seen, if fluid is introduced to the arrangement of FIG. 5,initially the fluid will enter through the connector 135, associatedwith the member 132, and will initially cause the shuttle 145 to movetowards the right until the stroke of the shuttle is complete. Therotatable assembly 140 will then rotate and fluid will then enterthrough the connector associated with the element 133 causing theshuttle to move towards the left, whilst simultaneously dispensing fluidpreviously introduced to the chamber 126 through the connector 138associated with the member 132. Once the illustrated arrangement hasreached a steady state of operation, a precisely metered quantity ofliquid will be dispensed during each stroke of the shuttle 145.

Referring to FIG. 6, an alternative embodiment of the invention isillustrated in which a valve arrangement is utilized which in somerespects is somewhat simpler than the valve arrangement utilized in theembodiments described above.

Referring to FIG. 6, a housing 150 is provided in the form of a block151 having a transversely extending bore 153. At one end the bore isclosed by a probe 154. The probe 154 is carried by an end plate 155secured to an end face of the block 151. The generally cylindrical probe154 extends from the end plate 155 into the bore. The probe 155terminates with an inner end portion 156 of reduced diameter. It can beseen that the probe 154 is fixed in position and is not adjustable.

At the other end of the bore, an adjustable probe 157 is provided, theprobe 157 incorporating a probe element 158 having a threaded portion159 on the exterior of the block 151, there being an adjusting nut 160on the threaded portion. The threaded portion 159 is inserted into athreaded end part 161 of the bore 153. The inner end portion of theprobe 162 is of reduced diameter.

It is to be noted that the probe 154 is provided with an electricalconductor 163 which extends to the inner end face of the probe, and theprobe 157 is provided with a conductor 164 which extends to the innerend of the probe.

A shuttle 165 is provided comprising a generally cylindrical body havingreduced diameter ends 166, 167. The shuttle is provided as a sealing fitwithin the chamber defined by the part of the bore 153 between theopposed inner ends of the probes 154, 157. At least the end faces of theshuttle are formed of conductive material.

The block 151 defines two transversely extending passages 168, 169. Thepassage 168 intersects the bore 153 and defines a flow port 170 in theside wall of the chamber 153. It can be seen that the reduced diameterend 162 of the probe 157 extends across the flow port. Similarly, thepassage 169 defines a flow port 171 and the probe 154 has the reduceddiameter end 156 thereof positioned to extend across the flow port 171.

The passage 168 is connected to a first three-way valve 172 which isadapted selectively to connect either a liquid entry conduit 173 to thepassage 178, or a liquid exit conduit 174 to the passage 168.

Similarly the passage 169 is connected to a three-way valve 175 adaptedto connect either a liquid exit passage 176 or a liquid inlet passage177 to the passage 169.

It is to be appreciated that the electrical conductors of the probeswill be connected to a control arrangement similar to that describedabove. In use of the valve shown in FIG. 6, with the shuttle 165 in theright-hand position as shown, the three-way valve 175 will be adjustedso that the liquid entry conduit 177 is connected to supply liquid tothe chamber defined by the bore 153, whilst the three-way valve 172connects the chamber to the liquid exit conduit 174. Liquid will flowthrough the three-way valve 175 into the chamber, moving the shuttle tothe left, and liquid will flow out of the chamber through the three-wayvalve 172 and into the liquid exit conduit 174. When the shuttle reachesthe left-hand-most position as shown in FIG. 6, the position of the twovalves is reversed and liquid from the liquid entry passage 173 willflow into the chamber moving the shuttle towards the left whilst liquidwill leave the chamber flowing through the valve 175 into the liquidexit passage 176.

FIG. 7 illustrates a further embodiment of the invention. In thisembodiment of the invention the unit 200 defines a block 201 defining anaxial bore 202. Mounted at a fixed position at one end of the bore 202is a fixed probe 203. The fixed probe 203 comprises an end, plate 204connected by means of a screw 205 to one end face of the block 201. Agenerally cylindrical probe portion 206 extends into the bore 202. Theprobe portion 206 has a reduced diameter end 207. An electricalconductor 208 is provided which extends axially of the probe andterminates at the end face of the reduced diameter portion 207.

At the opposite end of the bore, an adjustable probe is provided. Theadjustable probe comprises a generally cylindrical probe element 209,one end of which is provided with exterior threading 210. The exteriorthreading engages in a lock nut 211 provided on the exterior of theblock 201 and the terminal part of the threaded portion 210 also engageswith a threaded end region 212 of the bore 202. The inner end 213 of theprobe is of reduced diameter. A conductor 214 is provided which extendsaxially of the probe terminating at the end face of the reduced diameterportion.

A shuttle 215 is provided comprising a generally cylindrical body whichis a sliding sealing fit within the bore 202. The shuttle has reduceddiameter end faces 216. A chamber is defined by the portion of the bore202 between the inner ends of the two probes 203, 208. The first end ofthe chamber is associated with a transversely extending fluid entrypassage 217 which defines a fluid entry port 218 in the side wall of thechamber which contains the shuttle 214, there being a rotary ball valve219 provided in that passage 218 movable between the first position inwhich a fluid flow is permitted, and a second position in which a fluidflow is prevented. The other end of the chamber is associated with asecond fluid inlet passage 220 which forms a fluid inlet port 221 in theside wall of the chamber that contains the shuttle. The passage 220 isassociated with a ball valve 222 which is again movable from a positionin which it permits a fluid flow to a position in which no fluid flow ispermitted. The ball valves 219, 222 are driven by a common shaft 223 andare so located that when one valve is open to permit a fluid flow, theother valve is closed to prevent a fluid flow.

The first end of the chamber is also associated with a fluid exitpassage 224 which defines a fluid exit port 225 in the side wall of thechamber containing the shuttle 214. The fluid exit passage 224 isprovided with a ball valve 226 which, in one position permits a fluidflow and which, in an alternate position, does not permit a fluid flow.

The other end of the chamber is associated with a similar fluid exitpassage 227 which defines a fluid outlet port 228 in the side wall ofthe chamber that contains the shuttle. A further ball valve 229 isassociated with the passage 227, the ball valve being movable between aposition in which a fluid flow is permitted, and a position in which nofluid flow is permitted within the passage. The ball valve 229 and theball valve 226 are both driven by a common shaft 230, and thearrangement is such that when one valve is open, the other valve isclosed.

It is to be understood that the drive shafts 223 and 230 of the ballvalves will be driven in synchronism.

In operation of the arrangement shown in FIG. 7, it can be seen that theball valve 219 in the fluid entry passage 218 is open, and the ballvalve 229 in the fluid exit passage 227 is open. Fluid is thus, in theillustrated condition, entering the left-hand end of the chamber, asillustrated, and the shuttle 214 is moving towards the right. When theshuttle has moved a short distance, completing its stroke, the end faceof the reduced diameter end portion 216 of the shuttle 214 will contactthe probe 208 to generate a signal which will pass through the conductor214. Both of the shafts 223 and 230 will then be rotated to reverse theposition of the valves. The valve 222 in the fluid entry passage 220will then be open, whilst the ball valve 219 in the fluid entry passage218 will be closed. Similarly, the ball valve 229 in the fluid exitpassage 227 will be closed while the ball valve 226 in the fluid exitpassage 224 will be opened. Fluid will thus flow through the ball valve222 and through the fluid entry passage 220 into the right-hand end ofthe chamber, thus moving the shuttle 214 towards the left. Fluid willflow out of the fluid exit passage 224 passing through the ball valve226 until the shuttle has reached the left-hand-most position, when, asthe conductive end face of the reduced diameter portion 215 contacts theprobe 203, a signal passes through the electrical conductor 208. Theposition of the valves is then again reversed.

From the foregoing it can be seen that many embodiments of the inventionmay be devised which have different types of valve arrangement to shouldbe off-set by 360° relative to the other plurality. This will allow thearrangement to meter more often per revolution than that described indetail control the supply of fluid and the exit of fluid from thechamber carrying the shuttle.

Components of the devices described above may be made of ceramicmaterial to minimize problems of wear. The shuttle, in each embodiment,may be provided with a replaceable sleeve so that if the sleeve becomesworn it may be replaced.

It can readily be appreciated that devices of the type shown in FIG. 5,6 and 7 may be used in a metering arrangement of the kind shown in FIG.4.

In the described embodiments each probe carries an electric signal whenthe electrically conductive shuttle makes contact with the inner end ofthe probe within the chamber.

While the invention has been described with reference to an embodimentin which the rotor has one radial passage 41 to be aligned with thefirst inlet and the second outlet; and one radial passage 42 to bealigned with the second inlet and the first outlet with this arrangementthe rotor body 36 has to rotate 180° between cycles of operation. Thusit may be preferred to provide a plurality of angularly-spaced radialpassages aligned with the first inlet and second outlet and acorresponding plurality of radial passages aligned with the second inletand the first outlet. If the inlets and outlets are diametricallyopposed, it is preferred to use an odd number of passages, such asbetween three and seven or between five and nine passages. If fivepassages are used the rotor should be rotated 720° between cycles andthe passages of one plurality should be off-set by 36° relative to theother plurality. This will allow the arrangement to meter more often perrevolution than that described in detail above.

In order that this aspect of the invention may be more clearlyunderstood, reference is now made to FIGS. 8 and 9 of the accompanyingdrawings.

FIG. 8 is a schematic view illustrating an embodiment such as theembodiment of FIG. 1 showing the rotor of FIG. 1 in two alternatepositions. Thus in the embodiment of FIG. 1, a single inlet passage 320is connected to the connectors 26 associated with the two annularelements 15, 16. When the rotor of the apparatus of FIG. 1 is in thefirst position, as shown in FIG. 1, a first passage 41 formed at one endof the rotor is in alignment with the connector 26 of the annularelement 16, and the second radially extending passage 42 is in alignmentwith the connector 27 of the annular element 15. On rotation of therotor by 180°, the situation is reversed in that the first passage 41provided in the rotor is in alignment with the connector 27 of theannular 16 whereas the second radial passage 42 is in alignment with theconnector 26 of the annular element 15.

Referring now to FIG. 9, each rotor is provided with three radiallyextending passages. The radially extending passages on each rotor areequi-angularly spaced. The radially extending passages in the rotorassociated with the annular element 15, shown as the passages 51, 52,53, are evenly off-set relative to the passages associated with theannular element 16 which identified as passages 53, 54, 55. In theposition shown at the left-hand side of FIG. 10, the passage 54 isassociated with the connector 26 of the annular element 16, whereas thepassage 51 is associated with the connector 27 of the annular element15. On rotation of the rotor by 60°, a different situation obtains withthe passage 53 associated with the annular element 15 being in alignmentwith the connector 26 associated with that annular element, whereas thepassage 55 associated with the annular element 16 is in alignment withthe connector 27 of that annular element 16.

It is thus to be appreciated that when the shuttle has effected onemovement, the rotor only needs to be rotated by 60° to enable theshuttle to effect the reverse movement. This is in contrast with thearrangement shown in FIG. 9 where a rotation of 180° was necessary.

It is to be appreciated, therefore, that providing multiple passages, amore rapidly acting metering arrangement may be provided. It is,however, important that the number of radial passages provided at eachend of the rotor should be an odd number, and it is also desirable thatthe passages provided at one end of the rotor should be evenly off-setrelative to the passages at the other end of the rotor if the inlets andoutlets are diametrically opposed.

Referring now to FIG. 10 of the accompanying drawings, an arrangement isillustrated in which a metering valve 330 of the type shown in FIG. 1 isillustrated the metering valve having two outlets 331, 332, which arefed to a common stop valve 333. The stop valve is provided with acontrol 334. The control is adapted to open the stop valve 333 only whenthe rotor is in such a position that the radial passage within the rotoris in alignment with one of the two outlets from the metering valve 330,and with the other radial passage in communication with a supply ofpressurized fluid to be metered. Thus, in other words, the stop valve333 is only open when the shuttle is moving axially within the meteringvalve, thus dispensing metered fluid through either the outlet pipe 331or the outlet pipe 332, Preferably the arrangement is such that the stopvalve 333 is closed as soon as the shuttle has terminated its movementand thus the hydraulic pressure within the outlet pipes 331, 332 ismaintained at all times. This ensures that the entire system ismaintained in a “tight”condition. If no stop valve 333 were provided,fluid could drain away through the outlet pipes 331, 332 leading to anuneven or inaccurate metering.

FIG. 11 illustrates two metering valves 330 of the type shown in FIG.12, each having their outlets connected to a commonly operated stopvalve 333. Thus hydraulic integrity will be maintained in the outletsfrom the two metering valves 330. The outlet of the stop valve 333 isconnected to a static mixer 335. In this way accurate metered mixing maybe achieved.

FIG. 12 illustrates a metering valve which constitutes a furtherembodiment of the invention. The metering valve comprises a body 350having a planar upper surface 351. The upper part of the body defines anoutwardly extending flange 352. Mounted beneath the flange 352 is abearing 353 which supports annular drive gear 354 which totallysurrounds the body 350. The ring 354 carries a plurality of dependingdrive pins 355, the purpose of which will become clear from thefollowing description.

A lower part 366 of the body defines a frusto-conical exterior surface.The part 366 which defines the frusto-conical surface terminates in acylindrical depending neck 367 which is axially located. The lower partof the exterior of the neck is threaded 368.

A bore 369 is provided which extends axially through the neck 367 andaxially through the body 350. The upper end of the bore is provided withan adjustable probe 369 provided with electrodes 370. The lower end ofthe bore is scaled by an adjustable probe 371 with electrodes 372. Thebores and electrodes are similar to those described previously. Theupper part of the bore, adjacent the probe 369 is connected by means ofthe cranked passages 373 to points on the frusto-conical exterior of thebody 350 adjacent the neck 367. The lower part of the bore 369 adjacentthe probe 371 is connected by three radially outwardly extending passage374 (which are each diametrically opposite one of the passages 373) tofurther points on the frusto-conical exterior of the body 350, thesepoints being diametrically opposed to the points at which the fastpassages 373 reach the frusto-conical surface.

Thus the upper end of the bore defined between the probes is connectedto three points on the exterior of the frusto-conical surface, and thelower end of the bore is connected to a diametrically opposed points onthe frusto-conical surface.

The body 350 is provided with three equally angularly provided inletpassages, only one of which, 375, is shown in FIG. 12. The three inletpassages each extend vertically downwardly, each terminate at a point onthe frusto-conical surface of the body 350. The three inlet passages areequiangularly off-set.

The body 350 is also provided with three equi-angularly off-set outletpassages 3176, which again extend vertically, and the arrangement issuch that diametrically opposite each inlet passage 375 is an outletpassage 376.

It is to be appreciated that in alignment with each inlet passage 375,is a passage corresponding to the first passage 373 connected to theupper end of the bore adjacent the probe 369 and in alignment with eachoutlet passage 376 is a horizontal passage corresponding to passage 374.

A rotor 380 is provided defining a frusto-conical seat 391 which engageswith the frusto-cortical exterior surface of the part 366 of the body350. The rotor is mounted in position by means of bearings 382 whichengage the neck 367. A spring 383 engages part of the rotor 380 and alsoengages nut 384 provided for that purpose on the threading 368. Therotor 380 is thus biased so that the frusto-conical seat therein firmlyengages the frusto-conical exterior of the body 350. Defined in therotor are tow angular passage 385, 386. Each passage is such that, whenaligned therewith, it will interconnect an inlet 375 with the alignedpassage 373 or an outlet 376 with the aligned passage 374.1

Contained with the bore 369 between the probes is a shuttle 390. Theshuttle is provided with an exterior sleeve 391 formed of a materialwhich provides a good sliding fit within the bore. Should the material391 wear, that material may be replaced.

It is to be noted that the pins 355 provide don the drive gear 354engage recesses provided for that purpose in the rotor. Thus the rotormay be driven by driving the gear 354. With the rotor in an initialposition, as illustrated, fluid flowing through the inlet 37 r may passthrough the passage 385 defined in the rotor, and thus through thepassage 373 to the upper part of the bore, consequently forcing theshuttle 390 downwardly, forcing fluid through the passage 374 andthrough the outlet 376. When the rotor rotates by 60°, an inlet 375 willbe aligned with a passage corresponding to the passage 374 leading tothe lower part of the bore and an outlet will be aligned with thepassage corresponding to the passage 373 connected to the upper part ofthe bore and thus the shuttle will move in the opposite sense.

It is to be appreciated that the rotor will rotate only in response tothe shuttle physically contacting the probe at each end of the stroke,in the manner described above.

The stator 350 may be provided with a port 393 communicating with thespace between the two engaging frusto-conical fares. If there is anyweepage of liquid through the port 393, this will be a sign that themetering device is “wearing”.

Components of the devices described above may be made of a material tominimize wear.

In the present specification “comprise”means “includes or consists”and“comprising”means “including or consisting of”.

The features disclosed in the foregoing description, or the followingclaims, or the accompanying drawings, expressed in their specific formsor in term of a means for performing the disclosed function, or a methodor process for attaining the disclosed result, as appropriate, may,separately, or in any combination of such features, be utilized forrealizing the invention in diverse forms thereof.

I claim:
 1. A metering device comprising means defining a chambercomprised of two opposed ends comprising of elongate bore, each end ofthe elongate bore accommodating a respective probe, inner ends of whichbound the chamber, at least one probe being axially adjustable inposition, each probe comprising electrically conductive means extendingfrom the inner end face of the probe, inlet means to enable fluid toenter one end of the chamber and inlet means to enable fluid to enteranother end of the chamber, outlet means to enable fluid to exit fromsaid one end of the chamber, and outlet means to enable fluid to exitfrom the other end of the chamber, a shuttle provided within the chamberat a position intermediate said two ends, of the chamber at leastopposed ends of the shuttle being electrically conductive, the shuttleacting sealingly to separate two ends of the chamber, the shuttle beingmovable between two terminal positions, each probe being responsive tophysical contact with the shuttle to generate a respective electricsignal when the shuttle reaches each one of said two terminal positions,valve means to control fluid flow which, in one condition, permit theentry of fluid into one end of the chamber and permit the simultaneousexit of fluid from the other end of the chamber and which, in anothercondition, permit the entry of the fluid into said other end of thechamber and permit simultaneous exit of fluid from the said one end ofthe chamber, and control means adapted to change a condition of thevalve means on receipt of a said electric signal generated when theshuttle reaches a said terminal position.
 2. A metering device accordingto claim 1 wherein the inlet and outlet means incorporate ports in theside-wall of the chamber and the inner-most end of each probe whichdefines the chamber is configured to permit the entry or exit of fluidif the inner-most end of the probe is aligned with a said port.
 3. Ametering device according to claim 1 wherein said shuttle comprises acentral part which is a sealingly sliding fit within the chamber, andtwo terminal end parts of reduced diameter.
 4. A metering deviceaccording to claim 1, wherein said valve means is comprised of a rotorassembly, said rotor assembly being such that in one position thereof afluid flow is established between a first inlet and one end of thechamber, and is also established between the other end of the chamberand a first outlet, whereas in a second position of the rotor assemblyfluid flow is established between a second inlet and the other end ofthe chamber, and between said one end of the chamber and a secondoutlet, the rotor assembly being movable, by motor means, between saidpositions in response to a signal generated when the shuffle reaches oneof said terminal positions.
 5. A metering device according to claim 4,further comprising a housing comprised of a first inlet means and secondinlet means, first outlet means and second outlet means, said rotorassembly being rotatable within the housing, the rotor assemblycomprising an element defining the said chamber, and also defining afirst passage which extends from one end of the chamber and a secondpassage which extends from the other end of the chamber, the rotorassembly, in one position, having the first passage aligned with and incommunication with said first inlet, and said second passage alignedwith and in communication with said first outlet, and being rotatable toa second position in which said first passage is aligned with and incommunication with said second outlet and said second passage is inalignment with and in communication with said second inlet the saidpassages being substantially sealed in other positions of the rotor. 6.A metering device according to claim 5 wherein the rotor comprises afirst plurality of passages located to be aligned individually, onrotation of the rotor, with the first inlet and second outlet ad asecond plurality of passages located to be aligned individually, onrotation of the rotor, with the second inlet and first outlet.
 7. Ametering device according to claim 6 wherein said first plurality ofpassages and said second plurality of passages each comprise an oddnumber of passages, between five and nine.
 8. A metering deviceaccording to claim 5, wherein the rotor assembly comprises a bodyportion, said body comprising a central region with a relatively largediameter, the body tapering, from the central region of large diameter,towards opposed ends of the body, each tapering part of the body beingsnugly received within a co-operating frusto-conical or tapering openingformed in a respective annular element each annular element beingprovided with a respective said inlet and a respective said outlet.
 9. Ametering device according to claim 8 wherein said annular elements areretained within a housing, and means are provided to apply force to thefaces of the annular elements to bias the elements inwardly into securesealing contact with the tapering parts of the body.
 10. A meteringdevice according to claim 9 wherein the force applying means comprisemeans to apply hydraulic pressure to the end faces of the annularelements.
 11. A metering device according to claim 4, further comprisinga fixed body, the fixed body defining said chamber and defining firstinlet means, second inlet means, first outlet means and second outletmeans, each of said inlet means and outlet means terminating at anexterior surface of the body at a position adjacent the termination, atthe exterior of the body, of a respective passage leading to arespective end of the said chamber, the rotor assembly being mounted onthe exterior of the body, the rotor assembly comprising means which inone position of the rotor assembly, create a communication between thefirst inlet and the respective passage, and the second outlet and therespective passage and which, in an alternate position of the rotorassembly establish a connection between the second inlet and therespective passage, and the first outlet and the respective passage butwhich, in other positions of the rotor assembly, substantially seal saidinlets and said passages.
 12. A metering device according to claim 1,wherein said valve means comprise individual valves associated with saidinlet means and outlet means.
 13. A metering device according to claim1, wherein one end of the chamber is connected to a valve, the valvebeing adapted to connect said one end of the chamber selectively toeither a source of fluid to be introduced to the chamber, or to an exitconduit, the other end of the chamber being connected to a secondcorresponding valve adapted to connect the said other end of tilechamber selectively to either an exit conduit or a source of fluid to beintroduced to the chamber.
 14. A metering device according to claim 1,wherein each end of the chamber is associated with a respective entryconduit and exit conduit, each conduit having a respective valve tocontrol flow in the conduit.
 15. A device according to claim 1, furthercomprising a sensor is provided to sense fluid leaking from the deviceand to generate a signal indicative of the fluid leakage detected.
 16. Adevice according to claim 1, further comprising stop valve means in aflow path for fluid leaving the chamber, the stop valve means beingadapted to be opened only when the valve means permit flow from thechamber to the flow path.
 17. A metering device arrangement comprisingtwo metering devices according to claim 1, each metering device beingassociated with a reservoir of liquid to be metered by the meteringdevice, the outlets of the metering devices being directed to a mixeradapted to mix liquids from the reservoirs when metered by the devices,the control means of the metering devices each providing signals to asupervising control arrangement, the supervising control arrangementbeing adapted to stop the operation of one metering device in responseto a ceasing of the operation of the other metering device.
 18. Anarrangement according to claim 17 wherein the control means of eachmetering device pass a signal to the supervising control means onreceipt of a signal generated when a shuttle of the respective meteringdevice reaches a respective terminal position, the supervising controlmeans comprising counters adapted to count the signals, and means tocompare the counts present in the counters, the supervising controlfurther comprising means adapted to stop operation of the meteringdevices if an output from a comparator exceeds predetermined threshold.19. An arrangement according to claim 18 further comprising means tore-set the counters when the count in a counter exceeds a predeterminedthreshold.